13,224 research outputs found
Hard core attraction in hadron scattering and the family of the Ds meson molecule
We study the discovered Ds(2317) at BABAR, CLEO and BELLE, and find that it
belongs to a class of strange multiquarks, which is equivalent to the class of
kaonic molecules bound by hard core attraction. In this class of hadrons a kaon
is trapped by a s-wave meson or baryon. To describe this class of multiquarks
we apply the Resonating Group Method, and extract the hard core
kaon-meson(baryon)interactions. We derive a criterion to classify the
attractive channels. We find that the mesons f0(980), Ds(2457), Bs scalar and
axial, and also the baryons with the quantum numbers of Lambda, Xi_c, Xi_b and
also Omega_cc, Omega_cb and Omega_bb belong to the new hadronic class of the
Ds(2317).Comment: 5 pages, 1 figure, 2 tables, contribution to the X International
Conference on Hadron Spectroscopy, HADRON 2003, August 31 - September 6,
2003, Aschaffenburg, German
The Theta+ (1540) as an overlap of a pion, a kaon and a nucleon
We study the very recently discovered (1540) at SPring-8, at ITEP
and at CLAS-Thomas Jefferson Lab. We apply the same RGM techniques that already
explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon
exotic scattering, and the attractive hard core present in pion-nucleon and
pion-pion non-exotic scattering. We find that the K-N repulsion excludes the
Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as heptaquark,
equivalent to a N+pi+K borromean boundstate, with positive parity and total
isospin I=0. We find that the kaon-nucleon repulsion is cancelled by the
attraction existing both in the pion-nucleon and pion-kaon channels. Although
we are not yet able to bind the total three body system, we find that the
Theta+ may still be a heptaquark state.Comment: 5 pages, 3 figures, 1 table, contribution to the X International
Conference on Hadron Spectroscopy, HADRON 2003, August 31 - September 6,
2003, Aschaffenburg, German
Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations
Semiconducting nanoparticles are the building blocks of optical nanodevices
as their electronic states, and therefore light absorption and emission, can be
controlled by modifying their size and shape. CdSe is perhaps the most studied
of these nanoparticles, due to the efficiency of its synthesis, the high
quality of the resulting samples, and the fact that the optical gap is in the
visible range. In this article, we study light absorption of CdSe
nanostructures with sizes up to 1.5 nm within density functional theory. We
study both bulk fragments with wurtzite symmetry and novel fullerene-like
core-cage structures. The comparison with recent experimental optical spectra
allows us to confirm the synthesis of these fullerene-like CdSe clusters
Excitonic effects in the optical properties of CdSe nanowires
Using a first-principle approach beyond density functional theory we
calculate the electronic and optical properties of small diameter CdSe
nanowires.Our results demonstrate how some approximations commonly used in bulk
systems fail at this nano-scale level and how indispensable it is to include
crystal local fields and excitonic effects to predict the unique optical
properties of nanowires. From our results, we then construct a simple model
that describes the optical gap as a function of the diameter of the wire, that
turns out to be in excellent agreement with experiments for intermediate and
large diameters.Comment: submitte
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